Internal defibrillation is commonly indicated for shockable rhythm following cross-clamp removal in cardiac surgery. Low energy decreases the success rate of defibrillation but high energy can cause myocardial damage. This study aimed to determine the success rate of internal defibrillation for shockable arrhythmias after cardiac surgery.Retrospective data of 1,424 patients who developed shockable rhythms (ventricular fibrillation or ventricular tachycardia), and required internal defibrillation after aortic cross-clamp removal during cardiac surgery, without deep hypothermic circulatory arrest technique, from August 2015 to July 2017, were reviewed.The overall success rate of internal defibrillation in the first attempt of defibrillation was 61.5%. The success rate of the energy levels at 30, 10, and 7 Jules were 66.7, 64.9, and 61.5%, respectively. The success rate was higher in patients who had a better ejection fraction than those who failed after defibrillation. This was significantly associated with higher pH, higher bicarbonate, lower serum calcium, and lower total cardioplegic volume during cardiopulmonary bypass (CPB). Redo-valve surgery, valvular surgery, and combined coronary artery bypass graft with valvular surgery had a non-significantly lower success rate (p-value = 0.989). Incidence of failure for defibrillate patients in redo-valvular surgery, combined coronary artery bypass graft with valve surgery, adult congenital heart defect, and valvular surgery; requiring four or five shocks was non-significantly increased. Recurrent rate of ventricular fibrillation/ventricular tachycardia was 13.5%.The success rate of internal defibrillation was not related to the dose of energy used after being weaned off CPB.